The invention relates to a gear pump which is suitable for delivering highly viscous materials, such as caoutchouc mixtures.
Gear pumps permit a high output pressure while the stress to the material is low. The gear section is often used in combination with an extruder screw. German Patent document DE 100 49 730 A1 shows such a gear pump, in the case of which the material is supplied to a gear section with a planetary gear train by way of an input screw. The planetary gear train has a ring gear fixed to the casing and has four planet wheels which are rotatably disposed on a planet carrier. The planet carrier, in turn, is rotatably disposed in the ring gear and has four separating walls extending radially from a central basic body to the toothing of the ring gear, which separating walls form an inlet chamber element narrowing in the delivery direction and a pressure chamber element increasing in the delivery direction. Furthermore, in addition to this embodiment with the toothed ring gear and the non-toothed sun wheel with the planet carrier, the reverse arrangement is also mentioned, which requires higher expenditures, is rated to be more complex and has a toothed sun wheel and a ring gear operating as a function part with at least one sealing area, in the case of which the ring gear with the planet carrier can stand still.
In the case of the gear pump of German Patent document DE 100 49 730 A1, a high pumping capacity and self-cleaning is achieved by means of the planetary gear train. However, the bearing of the planetary gears on the planet carrier will then present problems when roller bearings are to be used because they cannot be sealed off sufficiently. Furthermore, the additional planet carrier with the sealing walls requires higher manufacturing expenditures and higher manufacturing costs.
European Patent document EP 0 642 913 B1 shows a single-shaft screw having two meshing gears, one of which is fitted onto the screw shaft. The gears are disposed to be fixed to the casing, in which case the bearing points are lubricated by the delivered highly viscous material. The pump casing is form-lockingly connected with the screw housing and consists of two figure-eight sealing disks which adjoin the faces of the two gears in a flush manner and are provided with openings for the passage of the screw shaft and the axle of the countergear. One product passage window respectively is provided on the sealing plates or on the screw housing at the level of the sealing plates, which product passage window is open toward the screw space. Such a gear pump permits a drive of the shaft gear by way of the screw shaft and a housing-fixed bearing of the countergear. However, the self-cleaning effect is low.
International Patent publication WO 00/53390 A1 shows a similar gear pump, in the case of which material is fed in the radial direction to two mutually meshing gears and is removed by way of an extruder screw connected with one of the gears. Here, a transfer mix area is provided in a starting area of the extruder screw. In this transfer mix area, a flight constructed in the extruder housing and extending in a helical manner and in the opposite direction with respect to the helical shape of the screw shaft decreases in its cross-section in favor of the enlarging screw shaft chamber. Such a transfer mix area, in addition to the delivery effect, causes a mixing of the highly viscous material. The material is fed from a common outlet of the mutually meshing gears into the flight of the transfer mix area and transferred into the enlarging screw shaft chamber. However, this requires a radial feeding of the material to be delivered. Furthermore, at most, an insufficient self-cleaning can be achieved.
It is an object of the invention to create improvements with respect to known gear pumps and particularly permit a good self-cleaning and a low-wear and low-maintenance bearing.
This object is achieved by means of a gear pump according to the invention. Preferred further developments are described and claimed herein.
According to the invention, an at least three-section gear pump is therefore provided which has a feeding and an output screw section, as well as a center gear section. The center gear section permits a high pump capacity and adjusting precision and prevents a reaction of the output section to pressure fluctuations of the input. The gear section according to the invention has planet wheels fixed to the housing and a sun wheel which is connected with the screw shafts in a rotationally fixed manner. In contrast to German Patent document DE 100 49 730 A1, the planet wheels, which are disposed in a fixed manner in the housing, can be disposed in the housing with low maintenance and low wear, particularly with roller bearings. The transfer mix areas in the input and output extruder achieve a mixing, in addition to the delivery.
For achieving a larger cross-section, the flights can be connected in the inlet area and outlet area respectively by way of connection ducts extending essentially in the circumferential direction.
In the following, the invention will be explained as an embodiment by means of the attached drawings.